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Abstract
Tremendous progress has been made in recent years in understanding the working of the living cell, including its micro-anatomy, signalling networks, and regulation of genes. However, an understanding of cellular phenomena using fundamental laws starting from first principles is still very far away. Part of the reason is that a cell is an active and exquisitely complex system where every part is linked to the other. Thus, it is difficult or even impossible to design experiments that selectively and exclusively probe a chosen aspect of the cell. Various kinds of idealised systems and cell models have been used to circumvent this problem. An important example is a giant unilamellar vesicle (GUV, also called giant liposome), which provides a cell-sized confined volume to study biochemical reactions as well as self-assembly processes that occur on the membrane. The GUV membrane can be designed suitably to present selected, correctly-oriented cell-membrane proteins, whose mobility is confined to two dimensions. Here, we present recent advances in GUV design and the use of GUVs as cell models that enable quantitative testing leading to insight into the working of real cells. We briefly recapitulate important classical concepts in membrane biophysics emphasising the advantages and limitations of GUVs. We then present results obtained over the last decades using GUVs, choosing the formation of membrane domains and cell adhesion as examples for in-depth treatment. Insight into cell adhesion obtained using micro-interferometry is treated in detail. We conclude by summarising the open questions and possible future directions.
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Affiliation(s)
- Susanne F Fenz
- Leiden Institute of Physics: Physics of Life Processes, Leiden University, The Netherlands
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52
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Balleza D. Mechanical properties of lipid bilayers and regulation of mechanosensitive function: from biological to biomimetic channels. Channels (Austin) 2012; 6:220-33. [PMID: 22790280 DOI: 10.4161/chan.21085] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Material properties of lipid bilayers, including thickness, intrinsic curvature and compressibility regulate the function of mechanosensitive (MS) channels. This regulation is dependent on phospholipid composition, lateral packing and organization within the membrane. Therefore, a more complete framework to understand the functioning of MS channels requires insights into bilayer structure, thermodynamics and phospholipid structure, as well as lipid-protein interactions. Phospholipids and MS channels interact with each other mainly through electrostatic forces and hydrophobic matching, which are also crucial for antimicrobial peptides. They are excellent models for studying the formation and stabilization of membrane pores. Importantly, they perform equivalent responses as MS channels: (1) tilting in response to tension and (2) dissipation of osmotic gradients. Lessons learned from pore forming peptides could enrich our knowledge of mechanisms of action and evolution of these channels. Here, the current state of the art is presented and general principles of membrane regulation of mechanosensitive function are discussed.
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Affiliation(s)
- Daniel Balleza
- Unidad de Biofísica, CSIC, UPV/EHU, Universidad del País Vasco, Leioa, Spain.
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53
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Smith AW. Lipid–protein interactions in biological membranes: A dynamic perspective. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:172-7. [DOI: 10.1016/j.bbamem.2011.06.015] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2011] [Revised: 06/21/2011] [Accepted: 06/23/2011] [Indexed: 01/31/2023]
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54
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Kuhn P, Eyer K, Robinson T, Schmidt FI, Mercer J, Dittrich PS. A facile protocol for the immobilisation of vesicles, virus particles, bacteria, and yeast cells. Integr Biol (Camb) 2012; 4:1550-5. [DOI: 10.1039/c2ib20181j] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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55
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Hansen JS, Vararattanavech A, Vissing T, Torres J, Emnéus J, Hélix-Nielsen C. Formation of giant protein vesicles by a lipid cosolvent method. Chembiochem 2011; 12:2856-62. [PMID: 22069223 DOI: 10.1002/cbic.201100537] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2011] [Indexed: 12/18/2022]
Abstract
This paper describes a method to create giant protein vesicles (GPVs) of ≥10 μm by solvent-driven fusion of large vesicles (0.1-0.2 μm) with reconstituted membrane proteins. We found that formation of GPVs proceeded from rotational mixing of protein-reconstituted large unilamellar vesicles (LUVs) with a lipid-containing solvent phase. We made GPVs by using n-decane and squalene as solvents, and applied generalized polarization (GP) imaging to monitor the polarity around the protein transmembrane region of aquaporins labeled with the polarity-sensitive probe Badan. Specifically, we created GPVs of spinach SoPIP2;1 and E. coli AqpZ aquaporins. Our findings show that hydrophobic interactions within the bilayer of formed GPVs are influenced not only by the solvent partitioning propensity, but also by lipid composition and membrane protein isoform.
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Affiliation(s)
- Jesper S Hansen
- Research Department, Aquaporin A/S, Ole Maaloes Vej 3, 2200 Copenhagen, Denmark.
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56
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Abstract
Biological research has always tremendously benefited from the development of key methodology. In fact, it was the advent of microscopy that shaped our understanding of cells as the fundamental units of life. Microscopic techniques are still central to the elucidation of biological units and processes, but equally important are methods that allow access to the dimension of time, to investigate the dynamics of molecular functions and interactions. Here, fluorescence spectroscopy with its sensitivity to access the single-molecule level, and its large temporal resolution, has been opening up fully new perspectives for cell biology. Here we summarize the key fluorescent techniques used to study cellular dynamics, with the focus on lipid and membrane systems.
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57
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Aimon S, Manzi J, Schmidt D, Poveda Larrosa JA, Bassereau P, Toombes GES. Functional reconstitution of a voltage-gated potassium channel in giant unilamellar vesicles. PLoS One 2011; 6:e25529. [PMID: 21998666 PMCID: PMC3188570 DOI: 10.1371/journal.pone.0025529] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2011] [Accepted: 09/05/2011] [Indexed: 11/19/2022] Open
Abstract
Voltage-gated ion channels are key players in cellular excitability. Recent studies suggest that their behavior can depend strongly on the membrane lipid composition and physical state. In vivo studies of membrane/channel and channel/channel interactions are challenging as membrane properties are actively regulated in living cells, and are difficult to control in experimental settings. We developed a method to reconstitute functional voltage-gated ion channels into cell-sized Giant Unilamellar Vesicles (GUVs) in which membrane composition, tension and geometry can be controlled. First, a voltage-gated potassium channel, KvAP, was purified, fluorescently labeled and reconstituted into small proteoliposomes. Small proteoliposomes were then converted into GUVs via electroformation. GUVs could be formed using different lipid compositions and buffers containing low (5 mM) or near-physiological (100 mM) salt concentrations. Protein incorporation into GUVs was characterized with quantitative confocal microscopy, and the protein density of GUVs was comparable to the small proteoliposomes from which they were formed. Furthermore, patch-clamp measurements confirmed that the reconstituted channels retained potassium selectivity and voltage-gated activation. GUVs containing functional voltage-gated ion channels will allow the study of channel activity, distribution and diffusion while controlling membrane state, and should prove a powerful tool for understanding how the membrane modulates cellular excitability.
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Affiliation(s)
- Sophie Aimon
- Unité Mixte de Recherche (UMR) 168, Physico-Chimie Curie, Centre National de la Recherche Scientifique (CNRS), Institut Curie, Centre de Recherche, Université Pierre et Marie Curie, Paris, France
| | - John Manzi
- Unité Mixte de Recherche (UMR) 168, Physico-Chimie Curie, Centre National de la Recherche Scientifique (CNRS), Institut Curie, Centre de Recherche, Université Pierre et Marie Curie, Paris, France
| | - Daniel Schmidt
- Howard Hughes Medical Institute, Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University, New York, New York, United States of America
| | | | - Patricia Bassereau
- Unité Mixte de Recherche (UMR) 168, Physico-Chimie Curie, Centre National de la Recherche Scientifique (CNRS), Institut Curie, Centre de Recherche, Université Pierre et Marie Curie, Paris, France
- * E-mail:
| | - Gilman E. S. Toombes
- Unité Mixte de Recherche (UMR) 168, Physico-Chimie Curie, Centre National de la Recherche Scientifique (CNRS), Institut Curie, Centre de Recherche, Université Pierre et Marie Curie, Paris, France
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58
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A single copy of SecYEG is sufficient for preprotein translocation. EMBO J 2011; 30:4387-97. [PMID: 21897368 DOI: 10.1038/emboj.2011.314] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Accepted: 07/15/2011] [Indexed: 11/08/2022] Open
Abstract
The heterotrimeric SecYEG complex comprises a protein-conducting channel in the bacterial cytoplasmic membrane. SecYEG functions together with the motor protein SecA in preprotein translocation. Here, we have addressed the functional oligomeric state of SecYEG when actively engaged in preprotein translocation. We reconstituted functional SecYEG complexes labelled with fluorescent markers into giant unilamellar vesicles at a natively low density. Förster's resonance energy transfer and fluorescence (cross-) correlation spectroscopy with single-molecule sensitivity allowed for independent observations of the SecYEG and preprotein dynamics, as well as complex formation. In the presence of ATP and SecA up to 80% of the SecYEG complexes were loaded with a preprotein translocation intermediate. Neither the interaction with SecA nor preprotein translocation resulted in the formation of SecYEG oligomers, whereas such oligomers can be detected when enforced by crosslinking. These data imply that the SecYEG monomer is sufficient to form a functional translocon in the lipid membrane.
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59
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Cirac AD, Moiset G, Mika JT, Koçer A, Salvador P, Poolman B, Marrink SJ, Sengupta D. The molecular basis for antimicrobial activity of pore-forming cyclic peptides. Biophys J 2011; 100:2422-31. [PMID: 21575576 DOI: 10.1016/j.bpj.2011.03.057] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2011] [Revised: 03/18/2011] [Accepted: 03/31/2011] [Indexed: 11/29/2022] Open
Abstract
The mechanism of action of antimicrobial peptides is, to our knowledge, still poorly understood. To probe the biophysical characteristics that confer activity, we present here a molecular-dynamics and biophysical study of a cyclic antimicrobial peptide and its inactive linear analog. In the simulations, the cyclic peptide caused large perturbations in the bilayer and cooperatively opened a disordered toroidal pore, 1-2 nm in diameter. Electrophysiology measurements confirm discrete poration events of comparable size. We also show that lysine residues aligning parallel to each other in the cyclic but not linear peptide are crucial for function. By employing dual-color fluorescence burst analysis, we show that both peptides are able to fuse/aggregate liposomes but only the cyclic peptide is able to porate them. The results provide detailed insight on the molecular basis of activity of cyclic antimicrobial peptides.
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Affiliation(s)
- Anna D Cirac
- Department of Biochemistry and Biophysical Chemistry, Groningen Biomolecular Sciences, Netherlands
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60
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Gornall JL, Mahendran KR, Pambos OJ, Steinbock LJ, Otto O, Chimerel C, Winterhalter M, Keyser UF. Simple reconstitution of protein pores in nano lipid bilayers. NANO LETTERS 2011; 11:3334-3340. [PMID: 21749149 DOI: 10.1021/nl201707d] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We developed a new, simple and robust approach for rapid screening of single molecule interactions with protein channels. Our glass nanopipets can be fabricated simply by drawing glass capillaries in a standard pipet puller, in a matter of minutes, and do not require further modification before use. Giant unilamellar vesicles break when in contact with the tip of the glass pipet and form a supported bilayer with typical seal resistances of ∼140 GΩ, which is stable for hours and at applied potentials up to 900 mV. Bilayers can be formed, broken, and re-formed more than 50 times using the same pipet enabling rapid screening of bilayers for single protein channels. The stability of the lipid bilayer is significantly superior to that of traditionally built bilayers supported by Teflon membranes, particularly against perturbation by electrical and mechanical forces. We demonstrate the functional reconstitution of the E. coli porin OmpF and α-hemolysin in a glass nanopipet supported bilayer. Interactions of the antibiotic enrofloxacin with the OmpF channel have been studied at the single-molecule level, demonstrating the ability of this method to detect single molecule interactions with protein channels. High-resolution conductance measurements of protein channels can be performed with low sample and buffer consumption. Glass nanopipet supported bilayers are uniquely suited for single-molecule studies as they are more rigid and the lifetime of a stable membrane is on the scale of hours, closer to that of natural cell membranes.
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Affiliation(s)
- Joanne L Gornall
- Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge, CB3 0HE, U.K
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61
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Abstract
Lipid and protein lateral mobility is essential for biological function. Our theoretical understanding of this mobility can be traced to the seminal work of Saffman and Delbrück, who predicted a logarithmic dependence of the protein diffusion coefficient (i) on the inverse of the size of the protein and (ii) on the "membrane size" for membranes of finite size [Saffman P, Delbrück M (1975) Proc Natl Acad Sci USA 72:3111-3113]. Although the experimental proof of the first prediction is a matter of debate, the second has not previously been thought to be experimentally accessible. Here, we construct just such a geometrically confined membrane by forming lipid bilayer nanotubes of controlled radii connected to giant liposomes. We followed the diffusion of individual molecules in the tubular membrane using single particle tracking of quantum dots coupled to lipids or voltage-gated potassium channels KvAP, while changing the membrane tube radius from approximately 250 to 10 nm. We found that both lipid and protein diffusion was slower in tubular membranes with smaller radii. The protein diffusion coefficient decreased as much as 5-fold compared to diffusion on the effectively flat membrane of the giant liposomes. Both lipid and protein diffusion data are consistent with the predictions of a hydrodynamic theory that extends the work of Saffman and Delbrück to cylindrical geometries. This study therefore provides strong experimental support for the ubiquitous Saffman-Delbrück theory and elucidates the role of membrane geometry and size in regulating lateral diffusion.
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62
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Wolters JC, Roelfes G, Poolman B. Design and synthesis of ATP-based nucleotide analogues and profiling of nucleotide-binding proteins. Bioconjug Chem 2011; 22:1345-53. [PMID: 21692528 DOI: 10.1021/bc100592q] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Two nucleotide-based probes were designed and synthesized in order to enrich samples for specific classes of proteins by affinity-based protein profiling. We focused on the profiling of adenine nucleotide-binding proteins. Two properties were considered in the design of the probes: the bait needs to bind adenine nucleotide-binding proteins with high affinity and carry a second functional group suitable and easily accessible for coupling to a chromatography resin. For this purpose, we synthesized p-biotinyl amidobenzoic acid-ATP (p-BABA-ATP) and p-biotinyl aminomethylbenzoic acid-ATP (p-BAMBA-ATP). p-BABA-ATP and p-BAMBA-ATP both bind to ATP-binding cassette (ABC) proteins with at least 10-fold higher affinity than ATP. Several ABC transporters could be enriched using p-BABA-ATP or p-BAMBA-ATP.
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Affiliation(s)
- Justina C Wolters
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Netherlands Proteomics Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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63
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van den Bogaart G, Thutupalli S, Risselada JH, Meyenberg K, Holt M, Riedel D, Diederichsen U, Herminghaus S, Grubmüller H, Jahn R. Synaptotagmin-1 may be a distance regulator acting upstream of SNARE nucleation. Nat Struct Mol Biol 2011; 18:805-12. [PMID: 21642968 PMCID: PMC3130798 DOI: 10.1038/nsmb.2061] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2010] [Accepted: 03/17/2011] [Indexed: 12/16/2022]
Abstract
Synaptotagmin-1 triggers Ca2+-sensitive, rapid neurotransmitter release by promoting the interaction of SNARE proteins between the synaptic vesicles and the plasma membrane. How synaptotagmin-1 promotes this interaction is controversial, and the massive increase in membrane fusion efficiency of Ca2+-synaptotagmin-1 has not been reproduced in vitro. However, previous experiments have been performed at relatively high salt concentrations, screening potentially important electrostatic interactions. Using functional reconstitution in liposomes, we show here that at low ionic strength SNARE-mediated membrane fusion becomes strictly dependent on both Ca2+ and synaptotagmin-1. Under these conditions, synaptotagmin-1 functions as a distance regulator: tethering the liposomes too far for SNARE nucleation in the absence of Ca2+, but brings the liposomes close enough for membrane fusion in the presence of Ca2+. These results may explain how the relatively weak electrostatic interactions of synaptotagmin-1 with membranes substantially accelerate fusion.
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Affiliation(s)
- Geert van den Bogaart
- Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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64
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AFM characterization of spin-coated multilayered dry lipid films prepared from aqueous vesicle suspensions. Colloids Surf B Biointerfaces 2011; 82:25-32. [DOI: 10.1016/j.colsurfb.2010.08.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2010] [Revised: 07/26/2010] [Accepted: 08/04/2010] [Indexed: 11/20/2022]
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65
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A Multiparametric Fluorescence Approach for Biomembrane Studies. ACTA ACUST UNITED AC 2011. [DOI: 10.1016/b978-0-12-387721-5.00005-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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66
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67
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Nikolaus J, Scolari S, Bayraktarov E, Jungnick N, Engel S, Pia Plazzo A, Stöckl M, Volkmer R, Veit M, Herrmann A. Hemagglutinin of influenza virus partitions into the nonraft domain of model membranes. Biophys J 2010; 99:489-98. [PMID: 20643067 DOI: 10.1016/j.bpj.2010.04.027] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2010] [Revised: 04/07/2010] [Accepted: 04/12/2010] [Indexed: 11/16/2022] Open
Abstract
The HA of influenza virus is a paradigm for a transmembrane protein thought to be associated with membrane-rafts, liquid-ordered like nanodomains of the plasma membrane enriched in cholesterol, glycosphingolipids, and saturated phospholipids. Due to their submicron size in cells, rafts can not be visualized directly and raft-association of HA was hitherto analyzed by indirect methods. In this study, we have used GUVs and GPMVs, showing liquid disordered and liquid ordered domains, to directly visualize partition of HA by fluorescence microscopy. We show that HA is exclusively (GUVs) or predominantly (GPMVs) present in the liquid disordered domain, regardless of whether authentic HA or domains containing its raft targeting signals were reconstituted into model membranes. The preferential partition of HA into ld domains and the difference between lo partition in GUV and GPMV are discussed with respect to differences in packaging of lipids in membranes of model systems and living cells suggesting that physical properties of lipid domains in biological membranes are tightly regulated by protein-lipid interactions.
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Affiliation(s)
- Jörg Nikolaus
- Department of Biology, Molecular Biophysics, Humboldt University Berlin, Berlin, Germany
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68
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Ramadurai S, Duurkens R, Krasnikov VV, Poolman B. Lateral diffusion of membrane proteins: consequences of hydrophobic mismatch and lipid composition. Biophys J 2010; 99:1482-9. [PMID: 20816060 PMCID: PMC2931744 DOI: 10.1016/j.bpj.2010.06.036] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2010] [Revised: 06/15/2010] [Accepted: 06/16/2010] [Indexed: 10/19/2022] Open
Abstract
Biological membranes are composed of a large number lipid species differing in hydrophobic length, degree of saturation, and charge and size of the headgroup. We now present data on the effect of hydrocarbon chain length of the lipids and headgroup composition on the lateral mobility of the proteins in model membranes. The trimeric glutamate transporter (GltT) and the monomeric lactose transporter (LacY) were reconstituted in giant unilamellar vesicles composed of unsaturated phosphocholine lipids of varying acyl chain length (14-22 carbon atoms) and various ratios of DOPE/DOPG/DOPC lipids. The lateral mobility of the proteins and of a fluorescent lipid analog was determined as a function of the hydrophobic thickness of the bilayer (h) and lipid composition, using fluorescence correlation spectroscopy. The diffusion coefficient of LacY decreased with increasing thickness of the bilayer, in accordance with the continuum hydrodynamic model of Saffman-Delbrück. For GltT, the mobility had its maximum at diC18:1 PC, which is close to the hydrophobic thickness of the bilayer in vivo. The lateral mobility decreased linearly with the concentration of DOPE but was not affected by the fraction of anionic lipids from DOPG. The addition of DOPG and DOPE did not affect the activity of GltT. We conclude that the hydrophobic thickness of the bilayer is a major determinant of molecule diffusion in membranes, but protein-specific properties may lead to deviations from the Saffman-Delbrück model.
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Affiliation(s)
| | | | | | - Bert Poolman
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Netherlands Proteomics Centre and the Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh, Groningen, The Netherlands
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69
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Sukhorukov VM, Dikov D, Busch K, Strecker V, Wittig I, Bereiter-Hahn J. Determination of protein mobility in mitochondrial membranes of living cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:2022-32. [PMID: 20655870 DOI: 10.1016/j.bbamem.2010.07.016] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2009] [Revised: 07/15/2010] [Accepted: 07/16/2010] [Indexed: 12/21/2022]
Abstract
Molecular mobility in membranes of intracellular organelles is poorly understood, due to the lack of experimental tools applicable for a great diversity of shapes and sizes such organelles can acquire. Determinations of diffusion within the plasma membrane or cytosol are based mostly on the assumption of an infinite flat space, not valid for curved membranes of smaller organelles. Here we extend the application of FRAP to mitochondria of living cells by application of numerical analysis to data collected from a small region inside a single organelle. The spatiotemporal pattern of light pulses generated by the laser scanning microscope during the measurement is reconstructed in silico and consequently the values of diffusion parameters best suited to the particular organelle are found. The mobility of the outer membrane proteins hFis and Tom7, as well as oxidative phosphorylation complexes COX and F(1)F(0) ATPase located in the inner membrane is analyzed in detail. Several alternative models of diffusivity applied to these proteins provide insight into the mechanisms determining the rate of motion in each of the membranes. Tom7 and hFis move along the mitochondrial axis in the outer membrane with similar diffusion coefficients (D=0.7μm(2)/s and 0.6μm(2)/s respectively) and equal immobile fraction (7%). The notably slower motion of the inner membrane proteins is best represented by a dual-component model with approximately equal partitioning of the fractions (F(1)F(0) ATPase: 0.4μm(2)/s and 0.0005μm(2)/s; COX: 0.3μm(2)/s and 0.007μm(2)/s). The mobility patterns specific for the membranes of this organelle are unambiguously distinguishable from those of the plasma membrane or artificial lipid environments: The parameters of mitochondrial proteins indicate a distinct set of factors responsible for their diffusion characteristics.
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Affiliation(s)
- Valerii M Sukhorukov
- Kinematic Cell Research Group, Institute for Cell Biology and Neurosciences, Goethe University, 60438 Frankfurt am Main, Germany.
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70
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Wang T, Ingram C, Weisshaar JC. Model lipid bilayer with facile diffusion of lipids and integral membrane proteins. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:11157-64. [PMID: 20459075 PMCID: PMC5814108 DOI: 10.1021/la101046r] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
A model membrane system is formed by the rupture of giant unilamellar vesicles (GUVs) onto a passivating layer comprising a PEG polymer cushion anchored in a lipid bilayer supported on glass. The novel use of pH-dependent electrostatic interactions between NeutrAvidin in the passivating layer and anionic lipids in the GUV drives vesicle rupture. The resulting "GUV pancakes" are single, planar lipid bilayer patches whose diameters vary from approximately 20 to 50 microm. The pancakes have several potential advantages for the in vitro study of protein-lipid interactions and integral membrane protein function. All components are commercially available. The pancakes resist nonspecific binding of vesicles containing protein. Both lipids and integral membrane proteins exhibit good lateral mobility in the GUV pancakes, as evidenced by single-particle tracking (SPT) of the DiD double-tailed fluorescent probe and of the integral membrane protein syntaxin-1A, labeled with AlexaFluor 633 (AF633-Syx). At least 80% of both probes exhibit free, homogeneous diffusion with a diffusion coefficient of approximately 5.5 microm(2) s(-1), which is more than 10 times faster than diffusion in a GUV pancake supported on bare glass. Atomic force microscopy (AFM) suggests that the polymer cushion has a height of approximately 4 nm. The mobility of a large fraction of the AF633-Syx probe suggests that even integral membrane proteins with large domains on both sides of the lipid bilayer should exhibit free diffusion within a GUV pancake.
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Affiliation(s)
- Tingting Wang
- Department of Chemistry, Graduate Program in Molecular Biophysics, 1101 University Avenue, University of Wisconsin—Madison, Madison, Wisconsin 53706
| | - Colin Ingram
- Department of Chemistry, Graduate Program in Molecular Biophysics, 1101 University Avenue, University of Wisconsin—Madison, Madison, Wisconsin 53706
| | - James C. Weisshaar
- Department of Chemistry, Graduate Program in Molecular Biophysics, 1101 University Avenue, University of Wisconsin—Madison, Madison, Wisconsin 53706
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71
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Macháň R, Hof M. Lipid diffusion in planar membranes investigated by fluorescence correlation spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:1377-91. [DOI: 10.1016/j.bbamem.2010.02.014] [Citation(s) in RCA: 197] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2009] [Revised: 02/10/2010] [Accepted: 02/10/2010] [Indexed: 11/25/2022]
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72
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Kahya N. Protein–protein and protein–lipid interactions in domain-assembly: Lessons from giant unilamellar vesicles. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:1392-8. [DOI: 10.1016/j.bbamem.2010.02.028] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2009] [Revised: 02/02/2010] [Accepted: 02/21/2010] [Indexed: 10/19/2022]
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73
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Stöckl M, Herrmann A. Detection of lipid domains in model and cell membranes by fluorescence lifetime imaging microscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:1444-56. [DOI: 10.1016/j.bbamem.2009.12.015] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Revised: 11/30/2009] [Accepted: 12/21/2009] [Indexed: 01/17/2023]
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74
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Gambin Y, Reffay M, Sierecki E, Homblé F, Hodges RS, Gov NS, Taulier N, Urbach W. Variation of the lateral mobility of transmembrane peptides with hydrophobic mismatch. J Phys Chem B 2010; 114:3559-66. [PMID: 20170092 DOI: 10.1021/jp911354y] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A hydrophobic mismatch between protein length and membrane thickness can lead to a modification of protein conformation, function, and oligomerization. To study the role of hydrophobic mismatch, we have measured the change in mobility of transmembrane peptides possessing a hydrophobic helix of various length d(pi) in lipid membranes of giant vesicles. We also used a model system where the hydrophobic thickness of the bilayers, h, can be tuned at will. We precisely measured the diffusion coefficient of the embedded peptides and gained access to the apparent size of diffusing objects. For bilayers thinner than d(pi), the diffusion coefficient decreases, and the derived characteristic sizes are larger than the peptide radii. Previous studies suggest that peptides accommodate by tilting. This scenario was confirmed by ATR-FTIR spectroscopy. As the membrane thickness increases, the value of the diffusion coefficient increases to reach a maximum at h approximately = d(pi). We show that this variation in diffusion coefficient is consistent with a decrease in peptide tilt. To do so, we have derived a relation between the diffusion coefficient and the tilt angle, and we used this relation to derive the peptide tilt from our diffusion measurements. As the membrane thickness increases, the peptides raise (i.e., their tilt is reduced) and reach an upright position and a maximal mobility for h approximately = d(pi). Using accessibility measurements, we show that when the membrane becomes too thick, the peptide polar heads sink into the interfacial region. Surprisingly, this "pinching" behavior does not hinder the lateral diffusion of the transmembrane peptides. Ultimately, a break in the peptide transmembrane anchorage is observed and is revealed by a "jump" in the D values.
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Affiliation(s)
- Yann Gambin
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Université Paris Diderot, CNRS, 24 rue Lhomond, 75005 Paris, France
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75
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Rayan G, Guet JE, Taulier N, Pincet F, Urbach W. Recent applications of fluorescence recovery after photobleaching (FRAP) to membrane bio-macromolecules. SENSORS 2010; 10:5927-48. [PMID: 22219695 PMCID: PMC3247740 DOI: 10.3390/s100605927] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Revised: 05/10/2010] [Accepted: 05/28/2010] [Indexed: 01/24/2023]
Abstract
This review examines some recent applications of fluorescence recovery after photobleaching (FRAP) to biopolymers, while mainly focusing on membrane protein studies. Initially, we discuss the lateral diffusion of membrane proteins, as measured by FRAP. Then, we talk about the use of FRAP to probe interactions between membrane proteins by obtaining fundamental information such as geometry and stoichiometry of the interacting complex. Afterwards, we discuss some applications of FRAP at the cellular level as well as the level of organisms. We conclude by comparing diffusion coefficients obtained by FRAP and several other alternative methods.
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Affiliation(s)
- Gamal Rayan
- Laboratoire de Physique Statistique de l'Ecole Normale Supérieure, associe aux Universites Paris 6 et Paris 7, CNRS UMR 8550, 24 rue Lhomond, 75005 Paris, France.
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76
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Shaklee PM, Semrau S, Malkus M, Kubick S, Dogterom M, Schmidt T. Protein incorporation in giant lipid vesicles under physiological conditions. Chembiochem 2010; 11:175-9. [PMID: 20013981 DOI: 10.1002/cbic.200900669] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Paige M Shaklee
- Physics of Life Processes, Leiden Institute of Physics, Leiden University, Niels Bohrweg 2, 2333 CA, Leiden, The Netherlands.
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77
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Nath S, Meuvis J, Hendrix J, Carl SA, Engelborghs Y. Early aggregation steps in alpha-synuclein as measured by FCS and FRET: evidence for a contagious conformational change. Biophys J 2010; 98:1302-11. [PMID: 20371330 PMCID: PMC2849099 DOI: 10.1016/j.bpj.2009.12.4290] [Citation(s) in RCA: 110] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2009] [Revised: 12/01/2009] [Accepted: 12/02/2009] [Indexed: 11/30/2022] Open
Abstract
The kinetics of aggregation of alpha-synuclein are usually studied by turbidity or Thio-T fluorescence. Here we follow the disappearance of monomers and the formation of early oligomers using fluorescence correlation spectroscopy. Alexa488-labeled A140C-synuclein was used as a fluorescent probe in trace amounts in the presence of excess unlabeled alpha-synuclein. Repeated short measurements produce a distribution of diffusion coefficients. Initially, a sharp peak is obtained corresponding to monomers, followed by a distinct transient population and the gradual formation of broader-sized distributions of higher oligomers. The kinetics of aggregation can be followed by the decreasing number of fast-diffusing species. Both the disappearance of fast-diffusing species and the appearance of turbidity can be fitted to the Finke-Watzky equation, but the apparent rate constants obtained are different. This reflects the fact that the disappearance of fast species occurs largely during the lag phase of turbidity development, due to the limited sensitivity of turbidity to the early aggregation process. The nucleation of the early oligomers is concentration-dependent and accompanied by a conformational change that precedes beta-structure formation, and can be visualized using fluorescence resonance energy transfer between the donor-labeled N-terminus and the acceptor-labeled cysteine in the mutant A140C.
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Affiliation(s)
- Sangeeta Nath
- Laboratory of Biomolecular Dynamics, Department of Chemistry & BioSCENTer, University of Leuven, Leuven, Belgium
| | - Jessika Meuvis
- Laboratory of Biomolecular Dynamics, Department of Chemistry & BioSCENTer, University of Leuven, Leuven, Belgium
| | - Jelle Hendrix
- Laboratory of Biomolecular Dynamics, Department of Chemistry & BioSCENTer, University of Leuven, Leuven, Belgium
| | - Shaun A. Carl
- Laboratory of Quantum and Physical Chemistry, Department of Chemistry, University of Leuven, Leuven, Belgium
| | - Yves Engelborghs
- Laboratory of Biomolecular Dynamics, Department of Chemistry & BioSCENTer, University of Leuven, Leuven, Belgium
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78
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Walde P, Cosentino K, Engel H, Stano P. Giant Vesicles: Preparations and Applications. Chembiochem 2010; 11:848-65. [DOI: 10.1002/cbic.201000010] [Citation(s) in RCA: 556] [Impact Index Per Article: 39.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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79
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Varnier A, Kermarrec F, Blesneac I, Moreau C, Liguori L, Lenormand JL, Picollet-D’hahan N. A Simple Method for the Reconstitution of Membrane Proteins into Giant Unilamellar Vesicles. J Membr Biol 2010; 233:85-92. [DOI: 10.1007/s00232-010-9227-8] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2009] [Accepted: 12/28/2009] [Indexed: 12/19/2022]
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80
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Macháň R, Hof M. Recent developments in fluorescence correlation spectroscopy for diffusion measurements in planar lipid membranes. Int J Mol Sci 2010; 11:427-457. [PMID: 20386647 PMCID: PMC2852847 DOI: 10.3390/ijms11020427] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Revised: 01/11/2010] [Accepted: 01/15/2010] [Indexed: 12/11/2022] Open
Abstract
Fluorescence correlation spectroscopy (FCS) is a single molecule technique used mainly for determination of mobility and local concentration of molecules. This review describes the specific problems of FCS in planar systems and reviews the state of the art experimental approaches such as 2-focus, Z-scan or scanning FCS, which overcome most of the artefacts and limitations of standard FCS. We focus on diffusion measurements of lipids and proteins in planar lipid membranes and review the contributions of FCS to elucidating membrane dynamics and the factors influencing it, such as membrane composition, ionic strength, presence of membrane proteins or frictional coupling with solid support.
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Affiliation(s)
- Radek Macháň
- J. Heyrovský Institute of Physical Chemistry of ASCR, v.v.i., Dolejškova 2155/3, 182 23 Prague, Czech Republic; E-Mail:
| | - Martin Hof
- J. Heyrovský Institute of Physical Chemistry of ASCR, v.v.i., Dolejškova 2155/3, 182 23 Prague, Czech Republic; E-Mail:
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81
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Ramadurai S, Holt A, Krasnikov V, van den Bogaart G, Killian JA, Poolman B. Lateral diffusion of membrane proteins. J Am Chem Soc 2009; 131:12650-6. [PMID: 19673517 DOI: 10.1021/ja902853g] [Citation(s) in RCA: 263] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We measured the lateral mobility of integral membrane proteins reconstituted in giant unilamellar vesicles (GUVs), using fluorescence correlation spectroscopy. Receptor, channel, and transporter proteins with 1-36 transmembrane segments (lateral radii ranging from 0.5 to 4 nm) and a alpha-helical peptide (radius of 0.5 nm) were fluorescently labeled and incorporated into GUVs. At low protein-to-lipid ratios (i.e., 10-100 proteins per microm(2) of membrane surface), the diffusion coefficient D displayed a weak dependence on the hydrodynamic radius (R) of the proteins [D scaled with ln(1/R)], consistent with the Saffman-Delbruck model. At higher protein-to lipid ratios (up to 3000 microm(-2)), the lateral diffusion coefficient of the molecules decreased linearly with increasing the protein concentration in the membrane. The implications of our findings for protein mobility in biological membranes (protein crowding of approximately 25,000 microm(-2)) and use of diffusion measurements for protein geometry (size, oligomerization) determinations are discussed.
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Affiliation(s)
- Sivaramakrishnan Ramadurai
- Department of Biochemistry, Groningen Biomolecular science and Biotechnology Institute & Zernike Institute of Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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82
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Ezanno P, Cribier S, Devaux PF. Asymmetrical stress generated by the erythrocyte lipid flippase triggers multiple bud formation on the surface of spherical giant liposomes. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:1277-80. [PMID: 19937014 DOI: 10.1007/s00249-009-0557-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2009] [Revised: 09/08/2009] [Accepted: 10/19/2009] [Indexed: 01/29/2023]
Abstract
Proteo-giant liposomes were electroformed from a mixture of lecithin vesicles and inside-out vesicles from erythrocytes. After addition of Mg-ATP in the vicinity of the proteo-giant liposomes, small buds appeared on the liposome surfaces, which--via an increase in lipids in the outer monolayer--demonstrated the active transport of lipids from the inner to the outer monolayer, indicating flippase activity.
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Affiliation(s)
- Pierre Ezanno
- Institut de Biologie Physico-Chimique, CNRS, UMR7099, 13 rue Pierre et Marie Curie, 75005, Paris, France
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83
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Kriegsmann J, Gregor I, von der Hocht I, Klare J, Engelhard M, Enderlein J, Fitter J. Translational diffusion and interaction of a photoreceptor and its cognate transducer observed in giant unilamellar vesicles by using dual-focus FCS. Chembiochem 2009; 10:1823-9. [PMID: 19551796 DOI: 10.1002/cbic.200900251] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
In order to monitor membrane-protein binding in lipid bilayers at physiological protein concentrations, we employed the recently developed dual-focus fluorescence correlation spectroscopy (2fFCS) technique. In a case study on a photoreceptor consisting of seven transmembrane helices and its cognate transducer (two transmembrane helices), the lateral diffusion for these integral membrane proteins was analyzed in giant unilamellar vesicles (GUVs). The two-dimensional diffusion coefficients of both separately diffusing proteins differ significantly, with D = 2.2 x 10(-8) cm2 s(-1) for the photoreceptor and with D = 4.1 x 10(-8) cm2 s(-1) for the transducer. In GUVs with both membrane proteins present together, we observed significantly smaller diffusion coefficients for labelled transducer molecules; this indicates the presence of larger diffusing units and therefore intermolecular protein binding. Based on the phenomenological dependence of diffusion coefficients on the molecule's cylindrical radius, we are able to estimate the degree of membrane protein binding on a quantitative level.
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Affiliation(s)
- Jana Kriegsmann
- Research Centre Jülich, ISB 2: Molecular Biophysics, 52425 Jülich, Germany
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84
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Boumann HA, Longo ML, Stroeve P, Poolman B, Hopmans EC, Stuart MC, Sinninghe Damsté JS, Schouten S. Biophysical properties of membrane lipids of anammox bacteria: I. Ladderane phospholipids form highly organized fluid membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:1444-51. [DOI: 10.1016/j.bbamem.2009.04.008] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2008] [Revised: 04/02/2009] [Accepted: 04/08/2009] [Indexed: 10/20/2022]
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85
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López-Esparza R, Guedeau-Boudeville M, Larios-Rodríguez E, Maldonado A, Ober R, Urbach W. Confinement of a hydrophilic polymer in membrane lyotropic phases. J Colloid Interface Sci 2009; 331:185-90. [DOI: 10.1016/j.jcis.2008.11.020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2008] [Revised: 11/08/2008] [Accepted: 11/11/2008] [Indexed: 11/15/2022]
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86
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Fluorescence correlation spectroscopy in membrane structure elucidation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:225-33. [DOI: 10.1016/j.bbamem.2008.08.013] [Citation(s) in RCA: 127] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2008] [Revised: 08/12/2008] [Accepted: 08/21/2008] [Indexed: 11/18/2022]
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87
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Battle AR, Petrov E, Pal P, Martinac B. Rapid and improved reconstitution of bacterial mechanosensitive ion channel proteins MscS and MscL into liposomes using a modified sucrose method. FEBS Lett 2008; 583:407-12. [DOI: 10.1016/j.febslet.2008.12.033] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2008] [Revised: 12/08/2008] [Accepted: 12/10/2008] [Indexed: 10/21/2022]
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88
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van den Bogaart G, Kusters I, Velásquez J, Mika JT, Krasnikov V, Driessen AJM, Poolman B. Dual-color fluorescence-burst analysis to study pore formation and protein-protein interactions. Methods 2008; 46:123-30. [PMID: 18667165 DOI: 10.1016/j.ymeth.2008.06.016] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2008] [Revised: 05/22/2008] [Accepted: 06/27/2008] [Indexed: 10/21/2022] Open
Abstract
Dual-color fluorescence-burst analysis (DCBFA) enables to study leakage of fluorescently labeled (macro) molecules from liposomes that are labeled with a second, spectrally non-overlapping fluorophore. The fluorescent bursts that reside from the liposomes diffusing through the focal volume of a confocal microscope will coincide with those from the encapsulated size-marker molecules. The internal concentration of size-marker molecules can be quantitatively calculated from the fluorescence bursts at a single liposome level. DCFBA has been successfully used to study the effective pore-size of the mechanosensitive channel of large-conductance MscL and the pore-forming mechanism of the antimicrobial peptide melittin from bee venom. In addition, DCFBA can be used to quantitatively measure the binding of proteins to liposomes and to membrane proteins. In this paper, we provide an overview of the method and discuss the experimental details of DCFBA.
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Affiliation(s)
- Geert van den Bogaart
- Department of Biochemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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89
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Fluorescence correlation spectroscopy for the study of membrane dynamics and protein/lipid interactions. Methods 2008; 46:116-22. [PMID: 18634881 DOI: 10.1016/j.ymeth.2008.06.011] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2008] [Revised: 05/27/2008] [Accepted: 06/05/2008] [Indexed: 11/22/2022] Open
Abstract
Fluorescence correlation spectroscopy (FCS) is a powerful technique to study dynamic biomolecular processes. It allows the estimation of concentrations, diffusion coefficients, molecular interactions, and other processes causing fluctuations in the fluorescence intensity, thus yielding information about aggregation processes, enzymatic reactions, or partition coefficients. During the last years, FCS has been successfully applied to model and cellular membranes, proving to be a promising tool for the study of membrane dynamics and protein/lipid interactions. Here we describe the theoretical basis of FCS and some practical implications for its application in membrane studies. We discuss sources of potential artifacts, such as membrane undulations, positioning of the detection volume, and photobleaching. Special attention is paid to aspects related to instrumentation and sample preparation as well as data acquisition and analysis. Finally, we comment on some strategies recently developed for the specific improvement of FCS measurements on membranes.
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90
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Sens P, Johannes L, Bassereau P. Biophysical approaches to protein-induced membrane deformations in trafficking. Curr Opin Cell Biol 2008; 20:476-82. [PMID: 18539448 DOI: 10.1016/j.ceb.2008.04.004] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2008] [Revised: 04/15/2008] [Accepted: 04/19/2008] [Indexed: 01/23/2023]
Abstract
Membrane traffic requires membrane deformation to generate vesicles and tubules. Strong evidence suggests that assembly of curvature-active proteins can drive such membrane shape changes. Well-documented pathways often involve protein scaffolds, in particular coats (clathrin or COP). However, membrane curvature should, in principle, be influenced by any protein binding asymmetrically on a membrane; large membrane morphological changes could result from their aggregation. In the case of Shiga toxin or viral matrix proteins, tubules and buds appear to result from the cargo-driven formation of protein-lipid nanodomains, showing that collective protein behaviour is crucial in the process. We argue here that a combination of in vitro experiments on giant unilamellar vesicles and theoretical modelling based on statistical physics is ideally suited to tackle these collective effects.
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Affiliation(s)
- Pierre Sens
- Laboratoire Gulliver, ESPCI, CNRS-UMR 7083, 10 rue Vauquelin, 75231 Paris Cedex 05, France
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91
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Doeven MK, van den Bogaart G, Krasnikov V, Poolman B. Probing receptor-translocator interactions in the oligopeptide ABC transporter by fluorescence correlation spectroscopy. Biophys J 2008; 94:3956-65. [PMID: 18212011 PMCID: PMC2367188 DOI: 10.1529/biophysj.107.120964] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2007] [Accepted: 12/21/2007] [Indexed: 11/18/2022] Open
Abstract
The oligopeptide transporter Opp is a five-component ABC uptake system. The extracytoplasmic lipid-anchored substrate-binding protein (or receptor) OppA delivers peptides to an integral membrane complex OppBCDF (or translocator), where, on ATP binding and hydrolysis, translocation across the membrane takes place. OppA and OppBCDF were labeled with fluorescent probes, reconstituted into giant unilamellar vesicles, and the receptor-translocator interactions were investigated by fluorescence correlation spectroscopy. Lateral mobility of OppA was reduced on incorporation of OppBCDF into giant unilamellar vesicles, and decreased even further on the addition of peptide. Fluorescence cross-correlation measurements revealed that OppBCDF distinguished liganded from unliganded OppA, binding only the former. Addition of ATP or its nonhydrolyzable analog AMP-PNP resulted in release of OppA from OppBCDF. In vanadate-trapped "transition state" conditions, OppA also was not bound by OppBCDF. A model is presented in which ATP-binding to OppDF results in donation of peptide to OppBC and simultaneous release of OppA. ATP-hydrolysis would complete the peptide translocation and reset the transporter for another catalytic cycle. Implications in terms of a general transport mechanism for ABC importers and exporters are discussed.
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Affiliation(s)
- Mark K Doeven
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747 AG Groningen, The Netherlands
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92
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Rosivatz E. Imaging the boundaries-innovative tools for microscopy of living cells and real-time imaging. J Chem Biol 2008; 1:3-15. [PMID: 19568794 PMCID: PMC2698318 DOI: 10.1007/s12154-008-0004-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2008] [Accepted: 03/11/2008] [Indexed: 01/17/2023] Open
Abstract
Recently, light microscopy moved back into the spotlight, which is mainly due to the development of revolutionary technologies for imaging real-time events in living cells. It is truly fascinating to see enzymes “at work” and optically acquired images certainly help us to understand biological processes better than any abstract measurements. This review aims to point out elegant examples of recent cell-biological imaging applications that have been developed with a chemical approach. The discussed technologies include nanoscale fluorescence microscopy, imaging of model membranes, automated high-throughput microscopy control and analysis, and fluorescent probes with a special focus on visualizing enzyme activity, free radicals, and protein–protein interaction designed for use in living cells.
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Affiliation(s)
- Erika Rosivatz
- Division of Cell and Molecular Biology, Imperial College London, SW7 2AZ, London, UK,
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93
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SNAREpin/Munc18 promotes adhesion and fusion of large vesicles to giant membranes. Proc Natl Acad Sci U S A 2008; 105:2380-5. [PMID: 18268324 DOI: 10.1073/pnas.0712125105] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Exocytic vesicle fusion requires both the SNARE family of fusion proteins and a closely associated regulatory subunit of the Sec1/Munc18 (SM) family. In principle, SM proteins could act at an early SNARE assembly step to promote vesicle-plasma membrane adhesion or at a late step to overcome the energetic barrier for fusion. Here, we use the neuronal cognates of each of these protein families to recapitulate, and distinguish, membrane adhesion and fusion on a novel lipidic platform suitable for imaging by fluorescence microscopy. Vesicle SNARE (v-SNARE) proteins reconstituted into giant vesicles ( approximately 10 mum) are fully mobile and functional. Through confocal microscopy, we observe that large vesicles ( approximately 100 nm) carrying target membrane SNAREs (t-SNAREs) both adhere to and freely move on the surface of the v-SNARE giant vesicle. Under conditions where the intrinsic ability of SNAREs to drive fusion is minimized, Munc18 stimulates both SNARE-dependent stable adhesion and fusion. Furthermore, mutation of a critical Munc18-binding residue on the N terminus of the t-SNARE syntaxin uncouples Munc18-stimulated vesicle adhesion from membrane fusion. We expect that the study of SNARE-mediated fusion with giant membranes will find wide applicability in distinguishing adhesion- and fusion-directed SNARE regulatory factors.
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94
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Sharonov A, Bandichhor R, Burgess K, Petrescu AD, Schroeder F, Kier AB, Hochstrasser RM. Lipid diffusion from single molecules of a labeled protein undergoing dynamic association with giant unilamellar vesicles and supported bilayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:844-850. [PMID: 18181653 DOI: 10.1021/la702600w] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
It is demonstrated that single-molecule tracking of a fluorescently labeled protein undergoing transient binding to model membranes presents a useful method of obtaining fluid properties. The labeled ACBP protein was tracked during its binding to free-standing giant unilamellar vesicles (GUVs) and supported bilayers prepared from the GUVs in the same environment. The analysis of images that are blurred as a result of fast probe diffusion was discussed. An examination of the lateral diffusion trajectories revealed a homogeneous diffusion on the top segments of the GUVs with D = 6.9 +/- 0.3 microm(2)/s. The supported bilayer experiments revealed two diffusion processes, one with Df = 3.1 +/- 0.4 microm(2)/s and the other with Ds = 0.078 +/- 0.001 microm(2)/s. The 2-fold difference in the lipid bilayer mobility for the free-standing and fast components in the supported bilayers is attributed to the known effect of frictional coupling with the solid support. The slow mobile fraction in the bilayer is suggested to be associated with the migration of pore-like structures, originating from the interaction of the membrane with the glass support.
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Affiliation(s)
- Alexey Sharonov
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
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95
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Geertsma ER, Nik Mahmood NAB, Schuurman-Wolters GK, Poolman B. Membrane reconstitution of ABC transporters and assays of translocator function. Nat Protoc 2008; 3:256-66. [DOI: 10.1038/nprot.2007.519] [Citation(s) in RCA: 196] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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96
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Jesorka A, Orwar O. Liposomes: technologies and analytical applications. ANNUAL REVIEW OF ANALYTICAL CHEMISTRY (PALO ALTO, CALIF.) 2008; 1:801-32. [PMID: 20636098 DOI: 10.1146/annurev.anchem.1.031207.112747] [Citation(s) in RCA: 335] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Liposomes are structurally and functionally some of the most versatile supramolecular assemblies in existence. Since the beginning of active research on lipid vesicles in 1965, the field has progressed enormously and applications are well established in several areas, such as drug and gene delivery. In the analytical sciences, liposomes serve a dual purpose: Either they are analytes, typically in quality-assessment procedures of liposome preparations, or they are functional components in a variety of new analytical systems. Liposome immunoassays, for example, benefit greatly from the amplification provided by encapsulated markers, and nanotube-interconnected liposome networks have emerged as ultrasmall-scale analytical devices. This review provides information about new developments in some of the most actively researched liposome-related topics.
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Affiliation(s)
- Aldo Jesorka
- Department of Chemical and Biological Engineering, Chalmers University of Technology, Göteborg, Sweden.
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97
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Chan YHM, Boxer SG. Model membrane systems and their applications. Curr Opin Chem Biol 2007; 11:581-7. [PMID: 17976391 DOI: 10.1016/j.cbpa.2007.09.020] [Citation(s) in RCA: 342] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2007] [Accepted: 09/28/2007] [Indexed: 10/22/2022]
Abstract
The complexity of biological membranes has motivated the development of a wide variety of simpler model systems whose size, geometry, and composition can be tailored with great precision. Approaches highlighted in this review are illustrated in Figure 1 including vesicles, supported bilayers, and hybrid membrane systems. These have been used to study problems ranging from phase behavior to membrane fusion. Experimental membrane models continue to advance in complexity with respect to architecture, size, and composition, as do computer simulations of their properties and dynamics. Analytical techniques such as imaging secondary ion mass spectrometry have also been developed and refined to give increasing spatial resolution and information content on membrane composition and dynamics.
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Affiliation(s)
- Yee-Hung M Chan
- Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA
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98
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Ursell T, Huang KC, Peterson E, Phillips R. Cooperative gating and spatial organization of membrane proteins through elastic interactions. PLoS Comput Biol 2007; 3:e81. [PMID: 17480116 PMCID: PMC1864995 DOI: 10.1371/journal.pcbi.0030081] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2007] [Accepted: 03/21/2007] [Indexed: 11/24/2022] Open
Abstract
Biological membranes are elastic media in which the presence of a transmembrane protein leads to local bilayer deformation. The energetics of deformation allow two membrane proteins in close proximity to influence each other's equilibrium conformation via their local deformations, and spatially organize the proteins based on their geometry. We use the mechanosensitive channel of large conductance (MscL) as a case study to examine the implications of bilayer-mediated elastic interactions on protein conformational statistics and clustering. The deformations around MscL cost energy on the order of 10 kBT and extend ∼3 nm from the protein edge, as such elastic forces induce cooperative gating, and we propose experiments to measure these effects. Additionally, since elastic interactions are coupled to protein conformation, we find that conformational changes can severely alter the average separation between two proteins. This has important implications for how conformational changes organize membrane proteins into functional groups within membranes. Membranes form flexible boundaries between the interior of a cell and its surrounding environment. Proteins that reside in the membrane are responsible for transporting materials and transmitting signals across these membranes to regulate processes crucial for cellular survival. These proteins respond to stimuli by altering their shape to perform specific tasks, such as channel proteins, which allow the flow of ions in only one conformation. However, the membrane is not just a substrate for these proteins, rather it is an elastic medium that bends and changes thickness to accommodate the proteins embedded in it. Thus, the membrane plays a role in the function of many proteins by affecting which conformation is energetically favorable. Using a physical model that combines membrane elastic properties with the structure of a typical membrane protein, we show that the membrane can communicate structural and hence conformational information between membrane proteins in close proximity. Hence, proteins can “talk” and “respond” to each other using the membrane as a generic “voice.” We show that these membrane-mediated elastic forces can ultimately drive proteins of the same shape to cluster together, leading to spatial organization of proteins within the membrane.
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Affiliation(s)
- Tristan Ursell
- Department of Applied Physics, California Institute of Technology, Pasadena, California, United States of America
| | - Kerwyn Casey Huang
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Eric Peterson
- Department of Physics, California Institute of Technology, Pasadena, California, United States of America
| | - Rob Phillips
- Department of Applied Physics, California Institute of Technology, Pasadena, California, United States of America
- Kavli Nanoscience Institute, Pasadena, California, United States of America
- * To whom correspondence should be addressed. E-mail:
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99
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Daniels DR, Turner MS. Diffusion on membrane tubes: a highly discriminatory test of the Saffman-Delbruck theory. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:6667-70. [PMID: 17489611 DOI: 10.1021/la0635000] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
The efficient transport of membrane proteins is vital in maintaining life. In this work, we investigate the transport of such membrane proteins along long thin membrane tubes or tethers. We calculate the diffusion constant to leading order in the low Reynolds number regime to be D = (4 pi eta)-1 log(r/a), with r and a being the tube and protein radii, respectively, and eta being the membrane viscosity. Thus we propose an exact limiting form for the controversial logarithmic correction, such as originally introduced by Saffman and Delbruck, that involves the tube radius rather than some "frame size". Our work suggests a test of this logarithmic correction could be achieved by measuring diffusion on membrane tubes, exploiting the fact that the equilibrium tube radius can be controlled by the membrane tension and varied over several orders of magnitude. We analyze the time taken for a protein to transit a membrane tube between cells and find that this can vary by an order of magnitude over physiological tensions. This is a strong effect in biological terms and suggests a possible regulatory coupling between membrane tension and signaling.
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Affiliation(s)
- D R Daniels
- Multidisciplinary Nanotechnology Centre, School of Engineering, University of Wales Swansea, Swansea SA2 8PP, UK
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100
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García-Sáez AJ, Schwille P. Single molecule techniques for the study of membrane proteins. Appl Microbiol Biotechnol 2007; 76:257-66. [PMID: 17497147 DOI: 10.1007/s00253-007-1007-8] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2007] [Revised: 04/17/2007] [Accepted: 04/17/2007] [Indexed: 11/26/2022]
Abstract
Single molecule techniques promise novel information about the properties and behavior of individual particles, thus enabling access to molecular heterogeneities in biological systems. Their recent developments to accommodate membrane studies have significantly deepened the understanding of membrane proteins. In this short review, we will describe the basics of the three most common single-molecule techniques used on membrane proteins: fluorescence correlation spectroscopy, single particle tracking, and atomic force microscopy. We will discuss the most relevant findings made during the recent years and their contribution to the membrane protein field.
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Affiliation(s)
- Ana J García-Sáez
- Biophysics Group, Biotechnologisches Zentrum (BIOTEC) der TU Dresden, Tatzberg 47-51, 01307 Dresden, Germany
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